Washington ? The White House on Monday protested what military officials called China’s harassment and aggressive shadowing of a U.S. Navy ocean surveillance ship in international waters Sunday, and it urged greater respect for maritime law.

Five Chinese vessels “surrounded” the USNS Impeccable in the South China Sea and closed within 50 feet, with Chinese crew members “waving Chinese flags and telling Impeccable to leave the area,” according to a Pentagon statement.

Impeccable sprayed fire hoses at one of the vessels in response, but the Chinese crew stripped to their underwear as their ship “continued closing to within 25 feet,” the Pentagon said.

At that point, Impeccable used a bridge-to-bridge radio to communicate its intent to move on. But two of the Chinese vessels stopped directly in the path of the U.S. ship, forcing it to conduct an emergency stop.

White House press secretary Robert Gibbs said the U.S. Navy will “continue to operate in those international waters, and we expect the Chinese to observe international law around there.”

The incident occurred about 75 miles south of Hainan Island, not far from where two Chinese fighters collided with a U.S. surveillance aircraft in international airspace in 2001, a few months after President Bush took office.

The U.S. Embassy in Beijing quickly lodged a formal protest over the incident with China’s Foreign Ministry, and senior Defense Department officials met Monday with a Chinese defense attache at the Pentagon to reiterate the objection, according to a defense official.

Under international law, the U.S. military can conduct activities “in waters beyond the territorial sea of another state without prior notification or consent” including in an exclusive economic zone of another country, said Maj. Stewart Upton, a Pentagon spokesman.

Navy ships and aircraft routinely operate in the area where the incident took place, Upton said.

The Impeccable and another ocean surveillance ship have been targeted five times in the last week, the Pentagon said, for “increasingly aggressive conduct” by Chinese ships and aircraft.

Last Thursday, a Chinese frigate crossed the Impeccable’s bow at a range of about 100 yards, the Pentagon said, and two hours later a Chinese Y-12 maritime surveillance aircraft conducted fly-bys of the U.S. ship at an altitude of 600 feet.

On Wednesday, the Pentagon said, a Chinese fisheries patrol vessel shone a high-intensity spotlight on the USNS Victorious, operating in the Yellow Sea, and the following day a Y-12 flew overhead at about 400 feet.